Ablation catheter with flexible electrode

ABSTRACT

A flexible tip electrode for an ablation catheter is disclosed. The catheter includes a catheter body and a hollow elongate tip electrode disposed at a distal end of the catheter body. The electrode includes a sidewall provided with one or more elongate gaps extending therethrough. The one or more elongate gaps providing flexibility in the sidewall for bending movement of the tip electrode relative to a longitudinal axis of the catheter body.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a Continuation of U.S. patent applicationSer. No. 15/348,823 filed Nov. 10, 2016, issued as U.S. Pat. No.10,188,459, which is a Continuation of U.S. patent application Ser. No.14/313,837 filed Jun. 24, 2014, issued as U.S. Pat. No. 9,510,903, whichis a Continuation of U.S. patent application Ser. No. 13/910,771 filedJun. 5, 2013, issued as U.S. Pat. No. 8,790,341, which is a Continuationof U.S. patent application Ser. No. 13/481,848 filed May 27, 2012,issued as U.S. Pat. No. 8,480,669, which is a Continuation of U.S.patent application Ser. No. 11/853,759 filed Sep. 11, 2007, issued asU.S. Pat. No. 8,187,267, which claims the benefit of U.S. ProvisionalApplication No. 60/939,799 filed May 23, 2007. The '459 patent, the '903patent, the '341 patent, the '669 patent, the '267 patent, and the '799application are hereby incorporated by reference as though fully setforth herein.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The field of the invention is catheters, specifically ablationcatheters.

(2) Background of the Invention

Ablation catheters with electrodes are generally known in the surgicalart, and ablation electrode catheters with irrigation capabilities arealso generally known in the art. Electrode catheters can be used forelectrically mapping a body part, or to deliver therapy to a body partor both.

Using ablation electrodes to create lesions in heart tissues is knownfor treating heart conditions such as arrhythmia. Linear lesions areknown to have some advantages over mere single point lesions. A singlepoint lesion, as its name implies, is created by applying energy at asingle point region of tissue. On the other hand, applying energy acrossan elongated region in a tissue creates a linear lesion.

Creating a linear lesion with only a tip electrode, however, isrelatively time-consuming, labor-intensive, and generally impractical. Asurgeon may use a typical single point electrode catheter to createlinear lesion, by carefully dragging the single point electrode tipacross the tissue while applying energy to the tissue surface.

U.S. Pat. No. 5,487,385, discloses a flexible catheter having ringelectrodes disposed along its flexible shaft for creating a linearlesion. A surgeon may lay such catheter shaft across a tissue area, andallow the consecutively-arranged ring electrodes to ablate the targettissue using RF energy. The ring electrodes, however, must applysufficient energy in order to create lesion areas that are connected,thus forming a single linear lesion. Applying too much RF energy,however, can cause unwanted damage. This arrangement often results in aseries of spaced-apart single point lesions.

U.S. Pat. No. 6,063,080 discloses a catheter having an elongatedelectrode. This electrode has micro-slotting or micro-apertures acrossits surface to improve flexibility of the electrode, thus allowing asurgeon to lay the elongated electrode across a tissue surface.

Despite some desirable properties, such a longitudinal type electrodehas several disadvantages. For example, the electrode requires aspherical structure at its tip to prevent the electrode from penetratingtissue. Also, a longitudinal type electrode cannot effectively create alinear lesion when the electrode is laid across a tissue having ridges.Thus, there is a continuing need for new ways to create linear lesions.

All referenced patents, applications and literatures are herebyincorporated by reference in their entirety. Furthermore, where adefinition or use of a term in a reference, which is incorporated byreference herein, is inconsistent or contrary to the definition of thatterm provided herein, the definition of that term provided hereinapplies and the definition of that term in the reference does not apply.The invention may seek to satisfy one or more of the above-mentioneddesire. Although the present invention may obviate one or more of theabove-mentioned desires, it should be understood that some aspects ofthe invention might not necessarily obviate them.

BRIEF DESCRIPTION OF THE INVENTION

Among the many different possibilities contemplated, embodiments offlexible tip electrodes for ablation catheters are disclosed. Thecontemplated flexible tip electrodes may have a dome-shaped tip. Acylindrical wall of the electrodes may have many openings extendingthrough the wall, and such contemplated openings can have variousshapes, sizes and overall configurations. The contemplated electrodesmay be coupled to an energy source for ablating tissues.

The contemplated openings perforate through the thickness of thecylindrical wall to improve flexibility of the electrode. In someembodiments, the openings in the wall provide sufficient gaps in thewall to allow shortening of a length of the electrode, when a force isapplied to the electrode in the linear direction, from its distal tiptowards its proximal end.

Among the many possible sizes, contemplated openings in the electrodewalls may have a width of between and including 0.01 to 0.50millimeters.

Contemplated electrodes may have flexibility in terms of flexing andbending along a longitudinal length of the electrode. An ability to flexallows the electrode to bend between and including 0.2 degrees to 70degrees, for example, along the longitudinal axis from a substantiallystraight position of the electrode. More specifically, the ability toflex may allow the tip electrode to bend between and including 5 degreesto 45 degrees along the longitudinal axis from a substantially straightposition of the electrode.

Contemplated openings in the electrodes may also create flexibility interms of shortening and lengthening the electrodes along thelongitudinal length of the electrodes. In one embodiment, the electrodemay shorten between and including 0.1% to 10% of a resting length of theelectrode. More specifically, the gaps in the electrode walls may allowshortening of the length between and including 0.5% to 5% of the length;even more specifically, the gaps in the walls may allow shortening ofthe length between and including 0.1% to 2% of the resting length; andeven shortening of the resting length between and including 0.1% to0.5%.

Further, it is contemplated that the electrodes may have flexibility interms of flexing and deforming the overall shape of the electrodes. Forexample, the electrodes may be deformed such that a cross sectionalshape of the electrode is changed. In one embodiment, the electrode maydeform like a marshmallow. Other embodiments only allow flexing andshortening, and do not deform like a marshmallow when subjected topressure.

Another aspect of the invention is directed to the pattern of theopenings in the electrodes. Contemplated electrodes may have at leastone opening forming a linear gap in the electrode wall. The pattern mayoptionally form the following types of gap configurations: a straightline, a zig-zag line, a line that outlines alternating interlockingblocks, an undulating line, and a wavy line.

In an exemplary embodiment, the contemplated patterns may outline aplurality of blocks in the wall disposed on both sides of a gap, andeach block may have a head and a neck, with the head being wider thanthe neck. Optionally, a first head of the block, which has a necksituated on one side of the gap, is disposed between a second and thirdheads both of which have necks positioned on the other side of the gap,and wherein the second and third heads have a shortest distance Abetween the two heads, with the distance A being shorter than a width ofthe first head.

Contemplated pattern of openings can also be described by focusing onthe structure defining the openings. For example, a contemplatedelectrode wall may be defined by a spiraling member. The member mayspiral about a longitudinal axis of the electrode forming a series ofloops, and the member may have a stem and a plurality of protrudingblocks disposed on both sides of the stem with each block extendingtransversely toward an adjacent loop. Contemplated blocks may havevarious shapes including a shape of an upside down triangle and bulbousshapes.

One embodiment includes a first head of a block disposed between asecond and third heads of two other blocks that are connected to anadjacent loop. In another embodiment, a distance B between the secondand third heads of an adjacent loop is shorter than a width of the firsthead, thereby restricting relative movement of two adjacent loops awayfrom each other. The member is contemplated to spiral about thelongitudinal axis with a pitch between and including 0.5 to 10 degrees.Similarly, the general layout of contemplated patterns of openings inpreferred embodiments is that the pattern spirals around the electrodewith a pitch between and including 0.5 to 10 degrees. Optimally, a pitchof approximately four degrees is desired. A pitch of approximately twodegrees is optimal. Generally, the higher the degree of pitch thestiffer the electrode becomes.

Contemplated electrodes may have gaps disposed between the first headand a stem of the adjacent loop, allowing freedom of movement of twoadjacent loops relative to each other.

In some embodiments, a coil may be disposed within the lumen to providestructural integrity to the electrodes. In still further embodiments,the coil may resiliently keep the electrode in a pre-determinedconfiguration. In one embodiment, the pre-determined configuration maybe straight. In another embodiment, the pre-determined configuration maybe an arcuate shape. The contemplated coil may resiliently bias theelectrode to stretch in a linear direction parallel to the longitudinalaxis of the electrode. It other words, the coil optionally biases thetip electrode to stretch lengthwise. Optionally, the coil, or theelectrode, or both, can be comprised of shape memory metal.

In still further other embodiments, the catheter may include irrigationfeatures, wherein a cooling fluid may be delivered in a lumen and passthrough the gaps to the outside of the electrode.

Various features, aspects and advantages of the present invention willbecome more apparent from the following detailed description along withthe accompanying drawings in which like numerals represent likecomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a flexible tipelectrode according to an aspect of the inventive subject matter.

FIGS. 1A-1C are alternative embodiments of the flexible tip electrodeshown in FIG. 1

FIG. 2 is a perspective view of another embodiment of a flexible tipelectrode according to an aspect of the inventive subject matter.

FIGS. 2A-2D are alternative embodiments of the flexible tip electrodeshown in FIG. 2.

FIG. 3 is a perspective view of another embodiment of a flexible tipelectrode according to an aspect of the inventive subject matter.

FIG. 3A is a side view of the embodiment shown in FIG. 3.

FIG. 4 is a perspective view of another embodiment of a flexible tipelectrode 20 according to an aspect of the inventive subject matter.

FIGS. 4A-4B are alternative embodiments of the flexible tip electrodeshown in FIG. 4.

FIG. 5 is a perspective view of another embodiment of a flexible tipelectrode according to an aspect of the inventive subject matter.

FIG. 6 is a perspective view of another embodiment of a flexible tipelectrode according to an aspect of the inventive subject matter.

FIGS. 7A-7C are illustrative views of some of the contemplatedembodiments of the invention in operation.

FIGS. 8A-8C are illustrative views of some of the contemplatedembodiments of the invention in operation.

FIG. 8D is a cross-sectional view of line A-A in FIG. 8B.

FIG. 8E illustrates electrode-to-surface area in FIG. 8C.

FIG. 9 is a side view of an embodiment of flexible tip electrode withinterlocking block pattern.

FIG. 9A is a close-up view of a block from the interlocking blockpattern of FIG. 9.

FIG. 10 is a view of a section of the electrode wall that makes up astem with interlocking blocks.

FIG. 11 is a view of an alternative design of bulbous interlockingblocks.

FIG. 12A is an illustrative view of the degree of pitch of the spiralingmember.

FIG. 12B is an illustrative view of the degree of flexing for theflexible tip electrode.

FIG. 12C is an illustrative view of an embodiment of the tip electrodebeing dragged across tissue with ridges.

FIG. 12D is an illustrative view of an embodiment of the tip electrodebeing dragged across smooth tissue surface.

FIG. 13 is a close-up view of one embodiment of the gap in the electrodewall.

FIG. 13A is a side view of the electrode in FIG. 13 at rest.

FIG. 13B is a side view of the electrode in FIG. 13 when pressed againsta tissue surface.

FIG. 14A is a longitudinal cross-sectional view of one embodiment of thetip electrode having a coil at rest.

FIG. 14B is a longitudinal cross-sectional view of another embodiment ofthe tip electrode having a coil with an arcuate shape at rest.

FIG. 15A is an illustrative view showing the shape and width of the gapas is cut by laser.

FIG. 15B is an illustrative view of showing a consistent width of thegap as is cut by laser.

FIG. 16 is a photograph of an embodiment of the present invention,illustrating size and dimension of interlocking blocks in relative tothe width of the catheter tip. The entire width of the catheter tip isshown.

FIG. 17 is a close-up photograph of an embodiment of the interlockingblocks. The entire with of the catheter tip is not shown here.

DETAILED DESCRIPTION OF THE INVENTION

The invention and its various embodiments can now be better understoodby turning to the following detailed description of numerousembodiments, which are presented as illustrative examples of theinvention defined in the claims. It is expressly understood that theinvention as defined by the claims may be broader than the illustratedembodiments described below.

Many alterations and modifications may be made by those having ordinaryskill in the art without departing from the spirit and scope of theinvention. Therefore, it must be understood that the illustratedembodiment has been set forth only for the purposes of example and thatit should not be taken as limiting the invention as defined by thefollowing claims. For example, notwithstanding the fact that theelements of a claim are set forth below in a certain combination, itmust be expressly understood that the invention includes othercombinations of fewer, more or different elements, which are disclosedherein even when not initially claimed in such combinations.

As used herein, the terms “spiral,” or “spiraling” in conjunction withelectrode wall and its patterns, refers to a circling configurationwhere a series of loops are formed. The loops have substantially thesame diameter, and resemble that of a coil. These terms do not refer tocircling on a same plane with increasing circumference.

As used herein, the terms “gap,” or “opening” in conjunction with acutting pattern in the electrode wall, refers to a perforation that ismore than a mere groove (which is only a surface cut that does not cutthrough the thickness of the wall). Gaps and openings are perforatedthrough the thickness of the electrode wall.

Embodiments of ablation catheters having a flexible tip electrode forcreating linear lesions in tissues are disclosed. The flexibility of thetip electrodes increases an electrode-to-tissue surface area, and inturn improves ablation of tissue. Especially in tissue where ridges arepresent, the flexible tip electrodes can be dragged across the ridgeswith improved continuous electrode-to-tissue contact.

Among the many different possibilities contemplated, the flexible tipelectrode for an ablation catheter is generally a hollow cylindricalstructure with a lumen. The tip electrode has a round dome-shapedterminal end. The cylindrical wall of the electrode may have manyopenings, and such openings can have various shapes, sizes and overallconfigurations.

Referring now to FIG. 1, an exemplary tip electrode 10 has a dome tip11, and has a 15 series of ring-like grooves 12 disposed about the tipelectrode, spaced equidistant from each other along a longitudinallength of the tip electrode. Each ring-like groove 12 may form acontinuous loop (as it is shown in FIG. 1A). Alternatively, all or partof the series of rings can be in a spiral configuration (as shown inFIG. 1B) around the outside surface of the tip electrode. In anotherembodiment, the electrode may include some rings that do not form acontinuous loop, but leaves the two terminal ends (13) of the groove (asshown in FIG. 1C) apart. A further embodiment may include a combinationof these configurations.

As used herein, the term “groove,” refers to a surface channel, and doesnot perforate through the wall of the electrode. In other embodiments,the grooves are replaced by cutting patterns that are thoroughlyperforated through the thickness of the wall of the electrode. In theembodiment shown in FIG. 1A, however, if each complete loop isthoroughly cut through, some type of additional supporting structure isrequired to connect the severed pieces together. For example, an innercoil may be provided within the lumen (see FIGS. 14A and 14B).

Referring now to FIG. 2, the grooves 12 are more spaced apart than thatshown in FIG. 1. Here, each ring-like groove does not form a continuousloop, and terminal ends 13 of each groove slightly offset each other tomaintain some degree of desired rigidity in the electrode. Note that inFIGS. 2A through 2B, the terminal ends 13 of the groove do not overlap.FIG. 2C illustrates another embodiment where the terminal ends 13 dooverlap, although they do not meet to form a continuous loop. Anothercontemplated embodiment may include a combination of grooves withoverlapping and grooves with non-overlapping terminal ends. As is truewith all embodiments disclosed in the instant application, grooves 12may be replaced with cutting patterns that are thoroughly perforatedthrough the thickness of the electrode wall.

FIG. 2D illustrates another embodiment where the ring-like grooves 12are half loops extending across about 180 degrees of the electrode'scylindrical surface. Many other positions of half loops are alsocontemplated. In other embodiments, some or all grooves may extendacross more or less than 180 degrees of the electrode's cylindricalcircumference.

In FIG. 3, three set of grooves 12 are provided, each set 14 having twonon-continuous loops. As shown in FIG. 3A, the two grooves 12 in asingle set 14 do not form a spiral. Spacing between the sets 14 isgenerally greater than spacing between the two loops in the same set.

In FIG. 4, another embodiment provides sections of ring-like grooves 12.In the embodiment shown in FIG. 4A, the rings are non-continuous loopsthat do not connect with each other. In the embodiment shown in FIG. 4B,each section is a spiral groove 12 collectively forming a continuousspiral groove.

FIG. 5, illustrates another embodiment with three sets of rings. Eachset 15 is shown to be a continuous spiral groove.

FIG. 6 illustrates another contemplated embodiment where a series ofring-like grooves 12 are disposed equidistant from each other along aproximal section of the tip electrode 10. Each ring may or may not forma continuous loop. Another embodiment provides that all or at least someof the groves each create a continuous loop. Embodiments applicable tothis Figure provide a desired rigidity in the distal portion of the tipelectrode 10.

FIGS. 7A through 7C illustrate embodiments of the invention in use. Oneaspect of the invention allows and facilitates dragging of the flexibletip electrode 10 across a tissue surface. Here, the flexible electrode10 deforms and/or flexes when it is dragged across a tissue surface. Theflexible and deformable properties of these embodiments create greaterelectrode-to-tissue surface area. In FIG. 7A, the tip electrode has acut pattern 12 that includes relatively straight lines that arethoroughly perforated through the thickness of the electrode. In FIG.7B, a tip electrode with zig-zag design cutting pattern allows evengreater flexibility that that of FIG. 7A. In FIG. 7C, however, thecatheter tip electrode has grooves at the neck region where theelectrode is attached to a catheter, allowing some degree of flexibilityin a more rigid tip electrode.

FIGS. 8A through 8E illustrate how some embodiments of the currentinvention may advantageously deform in other ways to create greaterelectrode-to-tissue surface area. In FIG. 8A, an embodiment of theelectrode is ready to make contact with tissue surface. The electrodemakes contact with tissue surface (FIG. 8B) and the tip electrodedeforms. A cross sectional area along line A-A becomes oval in shape(FIG. 8D). This embodiment not only flexes along a longitudinal axis,but also expands laterally. When the angle between the tissue surfaceand a longitudinal axis of the catheter body gets closer to a 90 degreeangle (FIG. 8C), the flexible tip deforms and shortens due to downwardpressure against the tissue surface. FIG. 8E shows a cross section ofthe tip electrode in FIG. 8C. The electrode-to-tissue surface area(represented by the circle in FIG. 8E) further expands outwardly(represented by arrows 16), as the catheter is pressed further towardsthe tissue surface. One contemplated embodiment that has the capabilityas shown in FIGS. 8A through 8E is the tip electrode with a zip-zag cutpattern as shown in FIG. 7B.

Referring now to FIG. 9, an exemplary embodiment of flexible tipelectrode 110 has a cutting pattern that outlines alternatinginterlocking blocks 117. In the illustrated embodiment, the contemplatedblocks 117 are disposed on both sides of the gap 118 created by thecutting pattern. Each block has a head 117A and a neck 117B, and thehead is wider than the neck. In this interlocking pattern, A first head(represented by “Y” in FIG. 9A) of the block 117, which has a neck 117Bsituated on one side of the gap 118, is disposed between a second andthird heads (represented by “X” in FIG. 9A), both of which have neckssituated on the other side of the gap 118. These blocks X and Y areinterlocked because the wider head portion of one head is locked betweenthe narrower neck portions of the two adjacent blocks 117. For example,the second and third heads X in FIG. 9A has a shortest distance A (shownas “A” in FIG. 9A) between the two heads, and distance A is shorter thana width (shown as “W” in FIG. 9A) of the first head Y.

Contemplated patterns of openings can also be described by focusing onthe structures of the electrode wall, instead of focusing on the shapeof the gap 118. For example, in FIG. 10, a contemplated electrode wallis comprised of a spiraling member 119. The member 119 spirals about alongitudinal axis of the electrode forming a series of loops (see FIG.9), and wherein the member 119 has a stem 119A and a plurality ofprotruding blocks 117 disposed on both sides of the member 119. Eachblock 117 transversely extends (see arrow T in FIG. 10) toward anadjacent loop in the electrode wall. Contemplated blocks can havevarious shapes. For example, at least some of the blocks may have ashape of an upside down triangle, where one angle of the trianglerepresents the neck region. Alternatively, blocks with bulbous shapesuch as ones shown in FIG. 11 may be utilized. Contemplated heads of thebulbous shapes are wider than their corresponding necks.

Referring back to FIG. 9A, this embodiment includes a first head (Y) ofa block 117 disposed between a second and third heads (X) of two otherblocks 117 that are connected to an adjacent loop. Further, a distance(A) between the second and third heads (X) of an adjacent loop isshorter than a width (W) of the first head (Y), thereby restrictingrelative movement of two adjacent loops away from each other.

The member 119, having an axis 119B, may spiral about the longitudinalaxis (“F” of FIG. 12) with a pitch (“P” of FIG. 12) between andincluding 0.5 to 10 degrees. To describe it in another way, the patternsof gaps 118 spirals around the longitudinal axis (“F”) with a pitchbetween and including 0.5 to 10 degrees.

The contemplated openings perforate through the thickness of thecylindrical wall to improve flexibility of the electrode. Theflexibility refers to flexing and bending along the longitudinal lengthof the electrode. For example, the ability to flex allows anapproximately 4 mm length of the electrode to bend in an angle G (seeFIG. 12B) that falls between and including 0.2 degrees to 70 degreesrelative to the longitudinal axis from a substantially straightposition. More specifically, the ability to flex allows theapproximately 4 mm length to bend between and including 5 degrees to 50degrees relative to the longitudinal axis from its substantiallystraight position. Even more specifically, the ability to flex allowsthe approximately 4 mm length to bend about 45 degrees relative to thelongitudinal axis from its substantially straight position.

FIGS. 12C and 12D illustrate an electrode 110 being dragged acrosstissue 130. In FIG. 12C, the electrode 110 is flexed and pressed againsttissue 130, which has a relatively irregular surface. Being able to flexprovides better contact with the target tissue, for example, in thetrabeculated endocardial tissue where there are valleys, ridges, andpockets. Here, electrode-to-tissue contact area is increased by usingthe side of the electrode 110 to deliver energy for ablation. Theincreased contact surface increases the likelihood of creating largerlesions at a given contact force and power setting. This enables deeperablation without having to increase the power setting, as higher powersetting undesirably increases the likelihood of coagulation. In FIG.12D, the dome tip 111 is used to delivery energy to tissue 130. Flexibleelectrode 110 absorbs any contraction or vibration of tissue 130, andimproves continuous tissue contact in a beating heart during systole anddiastole, whether the electrode contacts the tissue 130 in parallel,perpendicular, or every angle in-between orientation, or whether theelectrode is stationary at one location or when the electrode is inmotion being dragged. Without such flexibility, a standard rigid tipelectrode would “jump off” of the tissue in response to a beating heart.

Optionally, flexible electrode may have force-sensing capability tomeasure contact force in different directions. For example, a straingage, a fiber optic sensor, or other sensors 140 may be disposed withinthe electrode to measure amount of force causing the electrode to flex,and to shorten. Such data can be collected and transmitted to thephysician to monitor ablation progress. This may prevent accidentalpiercing of the target tissue when too much perpendicular force isapplied to press the dome 111 into the tissue.

Unlike known elongated electrodes (e.g., U.S. Pat. No. 6,063,080), whichcan be laid across a tissue to create relatively longer linear lesions,the current inventive subject matter has the unexpected advantage ofimproving precision in mapping and control at specific locations withinthe heart for more precise ablation, especially in relatively tightanatomical structures. Known elongated electrodes have difficultypositioning in such tight anatomical structures.

One unexpected advantage in having a flexible tip electrode is minimized“flipping.” When a standard rigid tip electrode is manipulated within acavity having valleys and pockets, the tip electrode can get caught inthe pocket when the physician continues to apply force in an attempt tomove the tip electrode. In such instance, a standard rigid tip electrodewould remain caught in the pocket until sufficient force is built, andthe tip electrode suddenly “flip” out of the pocket. Such “flipping” ishighly undesirable and should be avoided. The instant invention with aflexible tip greatly minimizes “flipping,” and allows smoother draggingacross valleys and pockets.

Referring now to FIG. 13, the openings in the wall provide a sufficientgap 118 in the wall to allow shortening of a length of the electrode,when a force is applied to the electrode in the linear direction. Thegap 118 disposed between a head 117A and a stem 119 of the adjacentloop, allows a freedom of movement (“F”) along the longitudinal axisbetween two adjacent loops relative to each other. Likewise, the gap 118between adjacent heads 117A provides a freedom of movement forlengthening of the electrode along the longitudinal length of theelectrode.

In one embodiment, the electrode can shorten between and including 0.2%to 10% of a resting length of the electrode. In one embodiment, the gapin the wall allows shortening of the length between and including 0.1%to 8% of the length. More specifically, the gap in the wall allowsshortening of the length between and including 0.5% to 5% of the length,and even more specifically, the gap in the wall allows shortening of thelength between and including 0.1% to 0.5% of the length.

In FIG. 13A, the electrode at rest has a freedom of movement (“F”)shown, because the electrode at rest assumes a pre-determined shapestretching in the “S” direction. When the electrode is applied to atissue 130, pressing force (arrows “P” in FIG. 13B) causes the electrodeto shorten, against the stretching force “S.” Once shortened, the widthof the gap illustrating freedom of movement (“F”) is minimized (see FIG.13B).

The stretching force “S” may be provided by a shape memory alloy in theelectrode 15 wall. Alternatively, FIG. 14A shows a cross sectional viewof an electrode where the stretching force “S” is provided by a coil 122in the lumen 120. The coil 122 provides structural integrity to theelectrode and resiliently keeps the electrode in a pre-determinedconfiguration at rest. In one embodiment, the pre-determinedconfiguration is straight. In another embodiment, the pre-determinedconfiguration at rest is an arcuate shape (see FIG. 14B). Thecontemplated coil resiliently biases the electrode to stretch in anendwise direction (“S” in FIG. 14A) parallel to the longitudinal axis ofthe electrode. It other words, the coil optionally biases the tipelectrode to stretch lengthwise.

The coil, or the electrode, or both, can include a shape memory metal.The flexible tip electrode can be made of suitable conductive andbiocompatible materials, suitable for ablation temperature; suchmaterials include natural and synthetic polymers, various metals andmetal alloys, Nitinol, naturally occurring materials, textile fibers,and all reasonable combinations thereof. In one embodiment, the tipelectrode includes MP3SN alloy.

The catheter can optionally couple to an irrigation system, wherein acooling fluid is 30 delivered in the lumen and allowed to pass throughthe gap to outside of the electrode. An internal irrigation system isalso possible. Also, the catheter can optionally couple to an energysource, such as a radio frequency (RF) generator to provide energyneeded for tissue ablation. An example of such RF generator is onedisclosed in U.S. Pat. No. 6,235,022.

Contemplated inventive subject matter also includes methods of making aflexible electrode for an ablation catheter by providing a hollowcylindrical electrode, and applying a laser to the cylindrical electrodeto cut through a wall of the electrode. The laser cuts the wall in apre-determined pattern that may continuously spiral around thecylindrical electrode. As shown in FIG. 15, the cut creates a gap 118that may be consistently wider in some sections (M) and narrower in someother sections (N). The wider sections (M) are substantially parallel toa longitudinal axis (119B in FIG. 12) of a spiral loop. The narrowersections (N) may connect wider sections (M) together, and may bedisposed generally transverse the longitudinal axis (119B) of the spiralloop.

The wider sections allow freedom of movement between adjacent spiralloops, making it possible to shorten the electrode when a force isapplied at a distal end of the electrode towards a proximal end.

FIG. 15B illustrates another embodiment where the laser also cuts thewall in a pre-determined pattern, where the gap 118 created by the laserhas generally consistent width. A coil is subsequently installed in thelumen of this electrode to provide stretching force to create widersections and narrower sections as illustrates in FIG. 15A.

Coatings such as gold and platinum can be applied to the electrode toincrease thermo-conductivity. The electrode can also be coated withheparin to provide anticoagulation effect. In addition, the electrodemay be electro-polished to reduce sharp edges.

The inventive subject matter also includes methods of performing linearablation using an embodiment of the present invention. As with typicalablation catheters, a physician can perform mapping using theelectrodes, and determine a target site for ablation. Once determined,the physician drags the flexible tip electrode across the target tissueto start ablation while applying energy to the tissue. Because theelectrode is flexible, the electrode can be more easily dragged acrosstissue surfaces having ridges and bumps while keeping constantelectrode-to-tissue contact. And because the gaps in the electrode wallallows the electrode to be shortened when pressed tip-down againsttissue surface, the chances of accidental tissue-piercing is lessened.

Thus, specific embodiments and applications of flexible tip electrodehave been disclosed. It should be apparent, however, to those skilled inthe art that many more modifications besides those already described arepossible without departing from the inventive concepts herein. Theinventive subject matter, therefore, is not to be restricted except inthe spirit of the appended claims.

The invention claimed is:
 1. An ablation catheter comprising a catheterbody and an electrode disposed at a distal end of the catheter body, theelectrode comprising an axial dimension extending along an axis and asidewall provided with one or more openings extending therethrough, thesidewall comprising a flexibility that allows shortening of theelectrode axial dimension when a force is applied to the electrode alongthe axis.
 2. The catheter as recited in claim 1, wherein the electrodefurther comprises a force-sensing member configured to provideinformation about the amount and direction of contact force exerted ontissue by the electrode.
 3. The catheter as recited in claim 1, whereinthe catheter further comprises a force-sensing capability configured todetermine contact force in different directions.
 4. The catheter asrecited in claim 1, wherein the catheter further comprises a fluiddelivery lumen in fluid communication with the one or more openings. 5.The catheter as recited in claim 1, wherein the electrode is configuredto deform and flex when it is dragged across a tissue surface.
 6. Thecatheter as recited in claim 1, wherein the electrode comprises aflexibility that enables it to radially deform such that a crosssectional shape of the electrode is changed.
 7. The catheter as recitedin claim 1, wherein the electrode comprises a flexibility that enablesthe sidewall to adopt different operating configurations relative to theaxis.
 8. The catheter as recited in claim 7, wherein the differentoperating configurations include at least one of a resting lengthconfiguration, a substantially straight configuration, andconfigurations having changed cross sectional shapes.
 9. The catheter asrecited in claim 1, wherein the sidewall is configured such that the oneor more openings enable bending movement of the electrode relative tothe axis of the electrode when the electrode impinges upon a tissuesurface, and configured for directed fluid egress from a portion of theopenings toward the tissue surface.
 10. The catheter as recited in claim1, wherein the openings provide an axial freedom of movement and areconfigured to allow the electrode to bend between about 5 degrees 50degrees relative to the axis of the electrode from its substantiallystraight position when the electrode impinges upon a tissue surface. 11.The catheter as recited in claim 1, wherein the electrode is configuredto deform when contact is made with a tissue surface parallel to theaxis such that the electrode-to-tissue surface area increases and theelectrode deforms laterally as the catheter is pressed further towardsthe tissue surface.
 12. The catheter as recited in claim 11, wherein theelectrode deforms like a marshmallow upon contact with the tissuesurface.
 13. An ablation catheter comprising a catheter body and anelectrode disposed at a distal end of the catheter body, the electrodecomprising an axial length along a longitudinal axis and a sidewallprovided with one or more openings extending therethrough, wherein theelectrode is configured to deform when contact is made with a tissuesurface parallel to the longitudinal axis such that theelectrode-to-tissue surface area increases and the electrode deformslaterally as the catheter is pressed further towards the tissue surface.14. The catheter as recited in claim 13, wherein the electrode furthercomprises a force-sensing member configured to provide information aboutthe amount and direction of contact force exerted on tissue by theelectrode.
 15. The catheter as recited in claim 13, wherein the catheterfurther comprises a force-sensing capability configured to determinecontact force in different directions.
 16. The catheter as recited inclaim 13, wherein the electrode is configured to deform and flex when itis dragged across a tissue surface.
 17. The catheter as recited in claim13, wherein the electrode comprises a flexibility that enables thesidewall to adopt different operating configurations relative to thelongitudinal axis, wherein the different operating configurationsinclude configurations having changed cross sectional shapes.
 18. Thecatheter as recited in claim 13, wherein the electrode deforms like amarshmallow upon contact with the tissue surface.
 19. An ablationcatheter comprising a catheter body and an electrode disposed at adistal end of the catheter body, the electrode comprising an axiallength along a longitudinal axis and a sidewall provided with one ormore openings extending therethrough, wherein the electrode comprises aflexibility that enables it to radially deform such that a crosssectional shape of the electrode is changed.
 20. The catheter as recitedin claim 19, wherein the electrode is configured to deform when contactis made with a tissue surface parallel to the longitudinal axis suchthat the electrode-to-tissue surface area increases and the electrodedeforms laterally as the catheter is pressed further towards the tissuesurface.
 21. The catheter as recited in claim 19, wherein the electrodefurther comprises a force-sensing member configured to provideinformation about the amount and direction of contact force exerted ontissue by the electrode.
 22. The catheter as recited in claim 19,wherein the catheter further comprises a force-sensing capabilityconfigured to determine contact force in different directions.
 23. Thecatheter as recited in claim 19, wherein the electrode is configured todeform and flex when it is dragged across a tissue surface.
 24. Thecatheter as recited in claim 19, wherein the openings provide an axialfreedom of movement and are configured to allow the electrode to bendbetween about 5 degrees 50 degrees relative to the longitudinal axis ofthe electrode from its substantially straight position when theelectrode impinges upon a tissue surface.
 25. The catheter as recited inclaim 19, wherein the sidewall is configured such that the one or moreopenings enable bending movement of the electrode relative to thelongitudinal axis of the electrode when the electrode impinges upon atissue surface.